Such devices are used for applying, to a particulate material, a surface layer of a coating agent intended to protect the enrobed particles from any external contaminants or to preserve their physical integrity. The coating agent may contain a dye and/or a substance conferring improved hardness and/or smoothing on the enrobed particles and a substance deferring in time the release of the active principle of a drug tablet. When such coating devices are used in the pharmaceutical industry for coating drug tablets, a coating device is generally disposed in a region situated between a region where a device is situated for de-dusting tablets after manufacture thereof from compressed drug powder and a region where a device is situated for packaging the coated tablets in suitable packaging.
Various types of device for coating particulate material and in particular pharmaceutical tablets exist according to the prior art: thus the patent application US 2010/0092694 A1 relates to a device for coating pharmaceutical tablets comprising a vertical chamber in which there is arranged a cylindrical tower comprising a central column to which there is fixed a continuous helical ramp for transporting the tablets to be coated from the base of the tower where they are introduced into the device as far as the top layer of where they are discharged after coating. The ascending movement of the tablets in the tower is obtained by vibration of the latter. During their rise along the ramp of the tower, the tablets are coated with coating agent sprayed by spray means oriented towards said ramp.
Such a device has the drawback that, since the particulate material to be coated is moved in the device in an ascending manner while the coating agent is sprayed thereon, the wetting of the material by the coating agent slows it in its rise since the wetted particles “skate” on the ramp of the tower, which causes localised conglomerations of this particulate material, such conglomerations being unfavourable to optimum coating since, in these conglomeration regions, the particulate material receives too much coating agent and the coated particles stick to one another there. Moreover, in a device according to the patent application in question, the particles to be coated have a tendency not to be exposed to the coating agent uniformly over their entire surface since they tend to keep their initial orientation during their rise.
The patent application US 366 820 solves this problem by proposing a device for spraying water onto rocky particles in order to wash these particles, in which they move by gravity on inclined flat tables disposed one above the other and are exposed to the spray when they fall from one table to the one underlying it.
Such a device has the drawback of being very bulky. This is because the particles move thereon by gravity and consequently it is necessary for the inclined tables that it comprises to be sufficiently inclined to ensure the movement in question, which gives rise to a significant height of the device for a given number of spray zones. Moreover, the device in question has a complex structure. This is because a frame peripheral to the device must be provided so that each of the aforementioned tables is fixed thereto.
WO 95/19838 responds to the aforementioned problem of conglomeration by proposing a device for coating particles with fertilising agent in which particles move by gravity on slightly inclined flat tables disposed one under the other and are coated with fertilising agent as they fall from one table to the one underlying it, by spray means disposed perpendicularly to the drop zone of said particles. To ensure correct movement of the particles while the tables that it comprises are slightly inclined, the device described requires that a means for fluidising said particles be provided, consisting of air injectors disposed under each table in order to project air through orifices arranged in these tables so as to fluidise thereon the particles in question so that they end up correctly in the drop zone in which they are coated with fertilising agent. The device in question therefore has the drawback of requiring a structure that is even more complex than the one of the device according to US 366 820.